1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same. More particularly, the present invention relates to a semiconductor module for a large power.
2. Description of the Prior Art
With the advancement of the technology of surface protection and resign sealing of a semiconductor chip, it became possible to miniaturize and simplify a semiconductor module for a large power, to enhance an insulating capability and to perform a composite integration of many functions and low cost of the semiconductor module. Although only about two years has passed since advent of such a semiconductor module for a large power, the module rapidly comes to be utilized in various fields.
FIG. 1 is a cross sectional view of a conventional semiconductor module for a large power. A tube 2 in rectangular section constituting a side portion of an outer container is fixed to a metal plate 1 for radiation by an adhesive material 3 such as an adhesive or an adhesive tape and is formed of a relatively low heat-proof resin for injection molding, such as PBT group resin, PPS group resin and phenol group resin and the like. A bed 4 for external electrodes, which is made of an insulating material, is fixed onto the metal plate 1 for radiation by an adhesive 3. External electrodes 5 are connected onto the underframe 4 by a soldering material 6. An alumina ceramic plate 8 on both sides of which metalized layers 9 are printed is connected onto the metal plate 1 for radiation by the soldering material 6. The alumina ceramic plate 8 insulates a power semiconductor chip 7 and effectively transfers a heat to the metal plate 1 for radiation. A heat sink plate 10 is connected onto the alumina ceramic plate 8 by the solder material 6 and a semiconductor chip 7 is connected to an upper surface of the heat sink plate 10. Aluminum leads 11 connect a semiconductor chip 7 to the external electrodes 5. The tube 2 is filled with a sealing resin 12 so that a semiconductor chip 7 is insulated and sealed and a mechanical stress applied to the aluminum leads 11 is reduced. The sealing resin may be a soft silicone group resin. A resin 13 for protection is applied on the sealing resin 12 so that the external electrodes 5 are fixed and protected from a mechanical action from the exterior. The resin 13 for protection may be a relatively hard epoxy group resin.
As described in the foregoing, a conventional apparatus is adapted such that the tube 2 and the bed 4 for exterior electrodes are separately adhered or soldered to the metal plate 1 for radiation, and hence the positioning and attachment of the respective parts take much time and also there are some problems about the respective adhesion and soldering. Particularly, since the outer container 2 is made from a synthetic resin and thus a brazing junction to the metal plate 1 for radiation is impossible, the container 2 is adhered to the plate 1 by an adhesive. In addition, the container 2 has a relatively large size and a complicated shape and hence a deformation due to thermal shrinkage occurs with ease. For this reason, a moisture from an exterior often penetrates into an interior from the adhered portion. For example, in a test in which a semiconductor device soaks in water of 2 kg/cm.sup.2 at 125.degree. C., which is one of accerelation tests for water immersion, the defect that deterioration of the semiconductor chip 7 and lowering of dielectric strength are caused within 50 to 100 hours is revealed.